First International Conference on MOLDAVIAN RISKS – FROM ...

<strong>First</strong> <strong>International</strong> <strong>Conference</strong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE
16-19 May 2012, Bacau, Romania
UPPER MANTLE STRUCTURES BENEATH THE
CARPATHIAN-PANNONIAN REGION: IMPLICATIONS FOR
ITS GEODYNAMICS
Yong Ren 1 , Graham W. Stuart 1 , Gregory A. Houseman 1 , Ben Dando 2 ,
Constantin Ionescu 3 , Endre Hegedüs 4 , Slavica Radovanović 5 , Yang Shen 6 ,
South Carpathian Project working group
1 School of Earth and Environment, University of Leeds, LS2 9JT, Leeds, UK;
2 RockTalk Imaging Ltd, Chacewater, Cornwall TR4 8PN, UK
3 National Institute of Earth Physics, Bucharest, Romania
4 Eötvös Loránd Geophysical Institute, Budapest, Hungary
5 Seismological Survey of Serbia, Belgrade, Serbia
6 Graduate School of Oceanography, University of Rhode Island, USA
Corresponding author: Yong Ren, earyr@leeds.ac.uk
Abstract: The Carpathian-Pannonian system of Eastern and Central Europe represents a
unique opportunity to study the interaction between surface tectonic processes involving
convergence and extension and convective processes in the upper mantle. Here, we
present high-resolution images of upper mantle structure beneath the region obtained using
P- and S-wave finite-frequency teleseismic tomography to help constrain the geodynamical
interpretation of the region. We have selected earthquakes with magnitude greater than 5.5
in the distance range 30°-95°, which occurred between 2006 and 2011. The data were
recorded on 57 temporary stations deployed in the South Carpathian Project (2009-2011),
56 temporary stations deployed in the Carpathian Basins Project (2005-2007), and 131
permanent broadband stations of national networks. The relative arrival times are
measured in high and intermediate frequency bands (0.5-2.0 Hz and 0.1-0.5 Hz for Pwaves,
0.1-0.5 Hz and 0.05-0.1 Hz for S-waves), and are inverted to produce P- and Swave
velocity maps in the upper mantle. Our images show a sub-vertical slab of fast
material beneath the eastern Alps which extends eastward across the Pannonian basin at
depths below ~300 km. The fast material extends down into the mantle transition zone
(MTZ), where it spreads out beneath the entire basin. Above ~300 km, the upper mantle
below the Pannonian basin is dominated by relatively slow velocities, the largest of which
extends down to ~200 km and underlies the >7km thick sediments of the Mako-Békés rift
basins. We suggest that cold mantle lithospheric downwelling occurred below the
Pannonian Basin before detaching in the mid-Miocene. In the Vrancea Zone, intermediatedepth
seismicity occurs at the NE end of an upper mantle high velocity structure that
extends SW oblique to the southern edge of the South Carpathians. This sub-vertical highvelocity
body is bounded by slow anomalies to the NW and SE, which extend down to the
top of the MTZ. No clear evidence of residual slabs is observed in the mid upper mantle
beneath Eastern Carpathians; the eastern Carpathians are underlain by slow velocities
everywhere above the transition zone. These observations suggest that intermediate depth
seismicity in the Vrancea Zone is unlikely to be due to slab tearing, but rather could be
explained by either gravitational instability or delamination of mantle lithosphere.
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